A self-assembled 3D Pt/TiO2 architecture for high-performance photocatalytic hydrogen production

Synthesis of Ag/Cu decorated 3D self-assembled nanowire TiO2 photocatalyst for hydrogen production: a promising pathway towards sustainable energy generation

Here, synthesis and characterization of TiO2 with different morphologies along with the cost-effective bimetallic decoration on optimized 3D self-assembled nanowire TiO2 (NWT) photocatalyst (Ag/Cu-NWT) with overwhelming hydrogen production rate is reported. All the photocatalysts were well characterized by different characterization techniques. Initially, the effect of morphology change obtained by changing the NaOH concentration has been studied for TiO2. Morphology obtained at 10 M NaOH solution, i.e., NWT (678 μmol/g), showed better hydrogen production than morphology obtained at 5 M (410 μmol/g), 15 M (210 μmol/g), and 20 M (160 μmol/g) NaOH solutions. Further, with the aim to achieve comparable or better activity low-cost photocatalyst as compared to Pt-TiO2 system, NWT was decorated with various Cu percentages and then with a minimal percentage of Ag on an optimized Cu-NWT photocatalyst. The observed trend for photocatalytic hydrogen production has been found to be P25 TiO2 < NWT < 1.0Cu-NWT < 0.5Pt-NWT ≤ 0.1Ag/1.0Cu-NWT. The marked increase by a factor of 103 in hydrogen production for the optimized bimetallic 0.1Ag/1.0Cu-NWT (10,184 μmol/g) photocatalyst compared to P25 TiO2 (99 μmol/g), nearly threefold increment in hydrogen production than an optimized 1.0 Cu-NWT (3907 μmol/g) photocatalyst and comparable hydrogen production as compared to 0.5Pt-NWT (10,050 μmol/g) may be attributed to the successful synthesis of a highly porous NWT morphology, which offers large surface area, increased light absorption combined with the synergistic effects of surface plasmon resonance (SPR), and the Schottky barrier for H+ reduction to H2 gas. The optimization of TiO2 morphology and an inexpensive bimetallic decoration strategy opens up promising opportunities for the development of cost-effective photocatalysts in the realm of energy and environment.

Self-Doped Carbon Dots Decorated TiO2 Nanorods: A Novel Synthesis Route for Enhanced Photoelectrochemical Water Splitting

Herein, we have successfully prepared self-doped carbon dots with nitrogen elements (NCD) in a simple one-pot hydrothermal carbonization method, using L-histidine as a new precursor. The effect of as-prepared carbon dots was studied for photoelectrochemical (PEC) water splitting by decorating NCDs upon TiO2 nanorods systematically by changing the loading time from 2 h to 8 h (TiO2@NCD2h, TiO2@NCD4h, TiO2@NCD6h, and TiO2@NCD8h). The successful decorating of NCDs on TiO2 was confirmed by FE-TEM and Raman spectroscopy. The TiO2@NCD4h has shown a photocurrent density of 2.51 mA.cm−2, 3.4 times higher than the pristine TiO2. Moreover, TiO2@NCD4h exhibited 12% higher applied bias photon-to-current efficiency (ABPE) than the pristine TiO2. The detailed IPCE, Mott–Schottky, and impedance (EIS) analyses have revealed the enhanced light harvesting property, free carrier concentration, charge separation, and transportation upon introduction of the NCDs on TiO2. The obtained results clearly portray the key role of NCDs in improving the PEC performance, providing a new insight into the development of highly competent TiO2 and NCDs based photoanodes for PEC water splitting.

Photocatalytic H2 Production from Naphthalene by Various TiO2 Photocatalysts: Impact of Pt Loading and Formation of Intermediates

This work presents a comparative study of the efficiency of two commercial TiO2 photocatalysts, Aeroxide P25 (ATiO2) and Sachtleben Hombikat UV100 (HTiO2), in H2 production from an aqueous solution of naphthalene. The TiO2 photocatalysts were platinized by the photodeposition method varying the platinum content of the suspension to 0.5, 1.0, and 5.0 wt%. A full physicochemical characterization for these materials was performed, showing no structural effects from the deposition method, and confirming a well dispersion of nanosized-Pt0 particles on the surface of both photocatalysts. Pristine ATiO2 shows around 14% higher photocatalytic fractional conversion of naphthalene than pristine HTiO2 after 240 min of irradiation, while both materials exhibit negligible activity for H2 formation. The 0.5 wt% Pt- HTiO2 increases the photocatalytic fractional conversion of naphthalene from 71% to 82% and produces 6 µmol of H2. However, using a higher Pt content than the optimal platinization ratio of 0.5 wt% dramatically inhibits both processes. On the other hand, regardless of the fractional ratio of Pt, the platinization of ATiO2 results in a decrease in the fractional conversion of naphthalene by 4% to 33% of the pristine value. Although the presence of Pt islands on the surface of the ATiO2 is essential for the H2 evolution, no dependency between the Pt ratio and the H2 formation rate was observed since all the platinized materials show a similar H2 formation of around 3 µmol. Based on the EPR results, the higher photocatalytic activity of the Pt-HTiO2 is attributed to the efficient charge carrier separation and its larger surface area. The recyclability test confirms that the inhibition of the photocatalytic process is related to the deactivation of the photocatalyst surface by the adsorption of the photoformed intermediates. A strong relationship between the photocatalytic activity and the kind of the aromatic compounds was observed. The H2 evolution and the photooxidation of the aromatic hydrocarbons exhibit higher photonic efficiencies than that of their corresponding hydroxylated compounds over the Pt-HTiO2.

Molybdenum disulfide quantum dots directing zinc indium sulfide heterostructures for enhanced visible light hydrogen production

Photocatalytic hydrogen (H₂) production based on semiconductors is important to utilize solar light for clean energy and environment. Herein, we report a visible light responsive heterostructure, designed and constructed by molybdenum disulfide quantum dots (MoS₂-QDs) in-situ seeds-directing growth and self-assemble of zinc indium sulfide (ZnIn₂S₄) nanosheet to ensure their full contact through a simple one-step solvothermal method for highly improved visible light H₂ production. The MoS₂-QDs in-situ seeds-directing ZnIn₂S₄ heterostructure not only builds heterojunctions between MoS₂ and ZnIn₂S₄ to spatially separate the photogenerated electrons and holes, but also serves as the active sites trapping photogenerated electrons to facilitate H₂ evolution. As a result, MoS₂-QDs/ZnIn₂S₄ exhibits high photocatalytic activity for H₂ production, and the optimized 2 wt% MoS₂-QDs/ZnIn₂S₄ (2MoS₂-QDs/ZnIn₂S₄) heterostructure exhibits the highest H₂ evolution rate of 7152 umol·h^-1·g^-1 under visible light, ∼9 times of pure ZnIn₂S₄. Our strategy here could shed some lights on developing noble-metal free heterostructures for highly efficient photocatalytic H₂ production.

Metal–organic framework assisted and in situ synthesis of hollow CdS nanostructures with highly efficient photocatalytic hydrogen evolution

Hollow CdS nanoboxes with a specific surface area of 153 m² g⁻¹ are synthesized through in situ sulfurizing Cd-MOF-47 with thiourea, which exhibit a greatly improved photocatalytic activity in water splitting to hydrogen (21 654 μmol g⁻¹ h⁻¹).

Novel mesoporous TiO2@g-C3N4 hollow core@shell heterojunction with enhanced photocatalytic activity for water treatment and H2 production under simulated sunlight

A novel mesoporous TiO₂@g-C₃N₄ hollow core@shell heterojunction photocatalyst was engineered for the first time by in situ calcining and growing of cyanamide (CY) on the surface of TiO₂. The HTCN-1 possesses good structure and performance when the addition amount of CY is 1 mL. HTCN-1 shows high photocatalytic activity toward congo red (CR), rhodamine B (RhB), phenol and ciprofloxacin (CIP) with degradation efficiencies of 97%, 100%, 73%, and 74%, respectively. HTCN-1 also displays high photocatalytic activity for H₂ generation at rate of 7.9 μmol h^-1. A possible charger transfer mechanism and photocatalytic degradation mechanism of HTCN-1 are proposed basing on the experiment results. The enhanced photocatalytic activity may be attributed to the higher charge transfer efficiency of photogenerated electron-hole (e^--h⁺) pairs caused by close contacts, a larger interfacial area, and the higher barrier for conduction bending. What's more, HTCN-1 possesses relatively high stability during the entire photoreaction process. Given the unique spatial structure and superior photocatalytic characteristics of the HTCN-1, there is great potential for applications in water treatment and H₂ generation.

Size-dependent activity and selectivity of carbon dioxide photocatalytic reduction over platinum nanoparticles

Platinum nanoparticles (Pt NPs) are one of the most efficient cocatalysts in photocatalysis, and their size determines the activity and the selectivity of the catalytic reaction. Nevertheless, an in-depth understanding of the platinum’s size effect in the carbon dioxide photocatalytic reduction is still lacking. Through analyses of the geometric features and electronic properties with variable-sized Pt NPs, here we show a prominent size effect of Pt NPs in both the activity and selectivity of carbon dioxide photocatalytic reduction. Decreasing the size of Pt NPs promotes the charge transfer efficiency, and thus enhances both the carbon dioxide photocatalytic reduction and hydrogen evolution reaction (HER) activity, but leads to higher selectivity towards hydrogen over methane. Combining experimental results and theoretical calculations, in Pt NPs, the terrace sites are revealed as the active sites for methane generation; meanwhile, the low-coordinated sites are more favorable in the competing HER.

Light-driven carbon dioxide conversion into fuels provides a nature-inspired strategy to combat climate change, but how materials do so remains a challenge. Here, the authors prepare metal–semiconductor composites and find platinum-nanoparticle size controls fuel selectivity and activity.

Pt-Enhanced Mesoporous Ti3+/TiO2 with Rapid Bulk to Surface Electron Transfer for Photocatalytic Hydrogen Evolution

Pt-doped mesoporous Ti³⁺ self-doped TiO₂ (Pt-Ti³⁺/TiO₂) is in situ synthesized via an ionothermal route, by treating metallic Ti in an ionic liquid containing LiOAc, HOAc, and a H₂PtCl₆ aqueous solution under mild ionothermal conditions. Such Ti³⁺-enriched environment, as well as oxygen vacancies, is proven to be effective for allowing the in situ reduction of Pt⁴⁺ ions uniformly located in the framework of the TiO₂ bulk. The photocatalytic H₂ evolution of Pt-Ti³⁺/TiO₂ is significantly higher than that of the photoreduced Pt loaded on the original TiO₂ and commercial P25. Such greatly enhanced activity is due to the various valence states of Pt (Ptⁿ⁺, n = 0, 2, or 3), forming Pt-O bonds embedded in the framework of TiO₂ and ultrafine Pt metal nanoparticles on the surface of TiO₂. Such Ptⁿ⁺-O bonds could act as the bridges for facilitating the photogenerated electron transfer from the bulk to the surface of TiO₂ with a higher electron carrier density (3.11 × 10²⁰ cm^-3), about 2.5 times that (1.25 × 10²⁰ cm^-3) of the photoreduced Pt-Ti³⁺/TiO₂ sample. Thus, more photogenerated electrons could reach the Pt metal for reducing protons to H₂.

Ultrathin Anatase TiO2 Nanosheets for High-Performance Photocatalytic Hydrogen Production

An ethanol solvothermal route has been developed to prepare ultrathin anatase TiO₂ nanosheets with dominant {001} facets (≈97%), a thickness of ≈2.5 nm, and a side length of ≈200 nm. The introduction of ethanol solvent significantly enhances the content of surface chemisorbed F^- on the TiO₂ nanosheet, which has a higher stability and further lowers the surface energy of {001} facets, giving rise to the large percentage of active {001} facets. Adopting well-defined morphology, such nanosheets loaded with 1 wt% Pt exhibit an H₂ evolution rate as high as 17.86 mmol h^-1 g^-1 , and the corresponding apparent quantum efficiency has been determined to be 34.2%.

Integrating metallic nanoparticles of Au and Pt with MoS2–CdS hybrids for high-efficient photocatalytic hydrogen generation via plasmon-induced electron and energy transfer

A mechanism of high-efficient photocatalytic hydrogen generation via plasmon-induced electron and energy transfer was demonstrated.

Controlled synthesis of CaTiO3:Ln3+ nanocrystals for luminescence and photocatalytic hydrogen production

Bifunctional CaTiO₃:Ln³⁺ nanocrystals not only can show very stable luminescence properties and a much higher quenching concentration due to the scheelite related structure of CaTiO₃, but also can exhibit a higher activity for hydrogen production.

The design of 3D artificial leaves with spatially separated active sites for H2 and O2 generation and their application to water splitting

TiO₂ artificial leaves with spatially separated CoO_x and Pt cocatalysts from biotemplates have been designed and exhibit enhanced photocatalytic hydrogen-production activity.

Green synthesis of Pt-doped TiO2 nanocrystals with exposed (001) facets and mesoscopic void space for photo-splitting of water under solar irradiation

We report a non-trivial facile chemical approach using ionic liquid ([bmim][Cl]) as a porogen for the synthesis of (001) faceted TiO2 nanocrystals having mesoscopic void space. This faceted TiO2 nanomaterial has been doped with Pt nanoclusters through chemical impregnation. The resulting Pt-doped TiO2 nanomaterials are thoroughly characterized by powder X-ray diffraction (PXRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), ultra high resolution transmission electron microscopy (UHR-TEM), energy dispersive X-ray spectrometry (EDX), UV-vis diffuse reflection spectroscopy (DRS) and N2 sorption studies. These Pt/TiO2 nanocrystals with (001) exposed facets are employed as efficient and benign catalysts for hydrogen production from pure water and methanol-water systems under one AM 1.5G sunlight illumination. The effect of platinum loading and methanol-water ratio on the photocatalytic activity of the faceted TiO2 nanocrystals are investigated and it is found that hydrogen evolution rates have been enhanced significantly upon Pt loading. Under optimized reaction conditions the highest photocatalytic activity of 11.2 mmol h(-1) g(-1) has been achieved over ca. 1.0 wt% Pt loaded Pt/TiO2 nanocrystals with (001) exposed facets, which is one of the highest hydrogen evolution rates over the noble metal/TiO2 system reported to date in the literature.

Structural design of TiO2-based photocatalyst for H2 production and degradation applications

This review aims to provide a comprehensive and contemporary overview, as well as a guide of the development of new generation TiO₂ based photocatalysts via structural design for improved solar energy conversion technologies.

π–π interactions mediated self-assembly of gold nanoparticles into single crystalline superlattices in solution

Self-assembly of colloidal gold nanoparticles employing π–π interactions in solution is studied. It is shown that capping ligand exchange with aromatic thiols results in formation of 3D single crystalline superlattices with long-range ordering.

Fabrication of ZnIn2S4–g-C3N4 sheet-on-sheet nanocomposites for efficient visible-light photocatalytic H2-evolution and degradation of organic pollutants

Novel ZnIn₂S₄–g-C₃N₄ sheet-on-sheet nanocomposites with excellent photocatalytic activities have been synthesized by a facile hydrothermal method.